JEE Mains Chemistry · Formula sheet

Biomolecules formulas

6 formulas, 10 reference tables and 47 common traps for JEE Mains Chemistry Biomolecules, grouped by subtopic.

Monosaccharides: Classification and Glucose Reactions

Reactions that prove the open-chain structure of glucose

Glucose with bromine water, nitric acid and acetic anhydride

\mathrm{CHO(CHOH)_4CH_2OH} \xrightarrow{\mathrm{Br_2\ water}} \mathrm{COOH(CHOH)_4CH_2OH} \qquad \mathrm{CHO(CHOH)_4CH_2OH} \xrightarrow{\mathrm{HNO_3}} \mathrm{COOH(CHOH)_4COOH} \qquad M_{\text{acetate}} = M_{\text{sugar}} + 42\,n_{\mathrm{OH}}

Classes of carbohydrates and their colour tests

Test	Reagent	Positive for	What you see
Fehling's	Copper(II) sulphate with sodium potassium tartrate in NaOH	Every reducing sugar	Red precipitate of Cu₂O
Benedict's	Copper(II) sulphate with sodium citrate and sodium carbonate	Every reducing sugar	Orange-red precipitate of Cu₂O
Tollens'	$\mathrm{[Ag(NH_3)_2]^+}$ in ammonia	Every reducing sugar, fructose included	Silver mirror
Barfoed's	Copper(II) acetate in dilute acetic acid	Reducing monosaccharides, within about two minutes	Red Cu₂O; reducing disaccharides react only after long heating
Seliwanoff's	Resorcinol in hydrochloric acid	Ketoses quickly; aldoses and pentoses only slowly	Cherry-red colour
Iodine	Iodine in potassium iodide solution	Starch	Blue-black colour
Biuret	Dilute copper(II) sulphate in NaOH	Two or more peptide bonds: proteins, tripeptides, biuret itself	Violet colour
Xanthoproteic	Concentrated nitric acid	Proteins with aromatic side chains	Yellow colour, orange with ammonia

Seliwanoff's and the iodine test use no copper; Fehling's, Benedict's, Barfoed's and the biuret test all do.

Common traps

Oligosaccharide units need not be identical

Only maltose gives two identical units. Sucrose gives glucose and fructose, and lactose gives galactose and glucose, so a statement that the units are always the same is false.

Fructose reduces Tollens' reagent without a CHO group

In alkaline solution fructose rearranges through an enediol to glucose and mannose, which carry CHO. So a ketose still gives the silver mirror, and every monosaccharide counts as reducing.

Seliwanoff's test uses no copper

Seliwanoff's reagent is resorcinol in hydrochloric acid; it works by dehydrating the sugar to a furfural that couples with resorcinol. Fehling's, Benedict's, Barfoed's and the biuret test all use copper(II).

Bromine water stops at one acid group

Bromine water oxidises only the CHO of glucose and gives gluconic acid, a monocarboxylic acid. The dicarboxylic saccharic acid needs nitric acid, which also oxidises the terminal CH₂OH.

Starch is hydrolysed by dilute acid

NCERT boils starch with dilute H₂SO₄ at 393 K under 2 to 3 atm to get glucose. A statement that uses concentrated sulphuric acid is false.

The acetate count is the OH count

A sugar that forms a tetraacetate has four OH groups and a pentaacetate five. Glucose pentaacetate has no free CHO, so it does not react with hydroxylamine or 2,4-DNP.

Cyclic Structures, D/L Configuration and Anomers

Learn this subtopic in the notes

D/L configuration from the Fischer projection

Stereocentres and stereoisomers of an open-chain sugar

k_{\text{aldose}} = n - 2 \qquad k_{\text{ketose}} = n - 3 \qquad N_{\text{stereoisomers}} = 2^{k}, \text{ half of them D}

Cyclic structures, anomers and epimers of glucose and fructose

Pair	Relationship	Where they differ
α-D-glucose and β-D-glucose	Anomers	Configuration at C-1 only
D-glucose and D-galactose	Epimers	Configuration at C-4 only
D-glucose and D-mannose	Epimers	Configuration at C-2 only
D-glucose and D-fructose	Functional isomers, both C₆H₁₂O₆	Aldehyde at C-1 against ketone at C-2
D-glucose and L-glucose	Enantiomers	Every stereocentre inverted
Glucose and ribose	Called homologous in some papers	Ribose has one CHOH unit fewer, C₅ against C₆ They differ by CH₂O, not by CH₂, so this is a paper's label, not a true homologous series.

Anomers differ at the anomeric carbon; epimers differ at any one other stereocentre.

Common traps

D and L are not the sign of rotation

D-glucose is dextrorotatory and D-fructose is laevorotatory. D or L comes from the position of the last stereocentre's OH; + or − comes from a polarimeter.

The terminal CH₂OH carbon is not a stereocentre

The reference is the last CHOH above the CH₂OH, not the CH₂OH itself. Counting the bottom carbon as a stereocentre turns a tetrose into a pentose and misreads the drawing.

L-glucose flips every OH

L-glucose is the mirror image of D-glucose, so its OH groups at C-2, C-3, C-4 and C-5 are all on the opposite side. Flipping only the C-5 OH gives a different sugar, L-idose.

The α anomer has the lower melting point and the higher rotation

α-D-Glucose melts at 419 K and rotates about +111°; β-D-glucose melts at 423 K and rotates about +19°. A statement that swaps either pair is false.

Fructose forms a five-membered ring

The C-5 OH of fructose adds to the C-2 ketone, so the ring holds four carbons and one oxygen: a furanose. In sucrose the fructose unit is β-D-fructofuranose.

Anomers and epimers are different pairs

α- and β-glucose differ at C-1, the anomeric carbon, so they are anomers. Glucose and galactose differ at C-4, so they are epimers, not anomers.

Disaccharides, Polysaccharides and Reducing Sugars

Learn this subtopic in the notes

Glycosidic linkages in sucrose, maltose and lactose

Disaccharide	Units on hydrolysis	Glycosidic link	Reducing?
Sucrose (cane sugar)	α-D-(+)-glucose and β-D-(−)-fructose	C-1 of glucose to C-2 of fructose, α1–β2	No
Maltose (malt sugar)	Two α-D-glucose units	C-1 of one glucose to C-4 of the next, α1–4	Yes
Lactose (milk sugar)	β-D-galactose and β-D-glucose	C-1 of galactose to C-4 of glucose, β1–4	Yes

Only sucrose joins two anomeric carbons, so only sucrose is non-reducing.

Starch, glycogen and cellulose: linkages and sources

Polysaccharide	Unit and linkage	Shape and solubility	Found in
Amylose	α-D-glucose, C-1 to C-4 only	Unbranched chain of 200 to 1000 units; soluble in water	Starch of plants, 15–20%
Amylopectin	α-D-glucose, C-1 to C-4 in chains, C-1 to C-6 at branches	Branched; insoluble in water	Starch of plants, 80–85%
Glycogen	α-D-glucose, C-1 to C-4 with C-1 to C-6 branches	More highly branched than amylopectin	Liver, muscles and brain of animals; yeast and fungi
Cellulose	β-D-glucose, C-1 to C-4 only	Straight chains packed side by side; insoluble in water	Plant cell walls; not digested by humans

Only cellulose has β links; only amylopectin and glycogen branch.

Common traps

A C-1 to C-4 link leaves one C-1 free

In maltose the first glucose uses its C-1, but the second glucose uses only its C-4. Its own C-1 stays a hemiacetal, so maltose is reducing. A statement calling maltose non-reducing is false.

Polysaccharides count as non-reducing

Starch and amylose have a single reducing end on a very long chain, so they give no Benedict's or Fehling's precipitate. Count them with sucrose, not with glucose.

Fructose, not glucose, is laevorotatory

Invert sugar is laevorotatory because fructose (−92.4°) rotates more strongly than glucose (+52.5°). A reason that gives the laevorotation to glucose is false.

Sucrose joins α-glucose to β-fructose

The link is C-1 of α-D-glucose to C-2 of β-D-fructose. A statement with β-glucose and α-fructose has the anomers swapped and is false.

Lactose uses C-1 of galactose

In lactose the galactose unit gives its anomeric C-1 and the glucose unit gives C-4. The reverse, C-1 of glucose to C-4 of galactose, is a common wrong option.

Amylose is the water-soluble fraction

NCERT calls amylose water soluble and amylopectin insoluble. An assertion that amylose is insoluble in water is false, even though amylose is indeed a long chain of 200 to 1000 glucose units.

Cellulose and starch differ in the anomer, not the carbons

Both join C-1 to C-4. Starch uses α-glucose and cellulose uses β-glucose. A polysaccharide described as having only β-glycosidic links is cellulose.

Amino Acids: Essential, Codes and Properties

Learn this subtopic in the notes

Structure, dipolar ion and chirality of α-amino acids

An α-amino acid and its dipolar ion

\mathrm{H_2N{-}CH(R){-}COOH} \;\rightleftharpoons\; \mathrm{H_3\overset{+}{N}{-}CH(R){-}COO^-}

The twenty amino acids: codes, side chains and the essential ones

Amino acid	Code	Side chain R	Class	Essential?
Glycine	G	$\mathrm{-H}$	Neutral	No
Alanine	A	$\mathrm{-CH_3}$	Neutral	No
Valine	V	$\mathrm{-CH(CH_3)_2}$	Neutral	Yes
Leucine	L	$\mathrm{-CH_2CH(CH_3)_2}$	Neutral	Yes
Isoleucine	I	$\mathrm{-CH(CH_3)CH_2CH_3}$	Neutral	Yes
Arginine	R	$\mathrm{-(CH_2)_3NHC(=NH)NH_2}$	Basic	Yes
Lysine	K	$\mathrm{-(CH_2)_4NH_2}$	Basic	Yes
Glutamic acid	E	$\mathrm{-CH_2CH_2COOH}$	Acidic	No
Aspartic acid	D	$\mathrm{-CH_2COOH}$	Acidic	No
Glutamine	Q	$\mathrm{-CH_2CH_2CONH_2}$	Neutral	No
Asparagine	N	$\mathrm{-CH_2CONH_2}$	Neutral	No Its amide N is not basic, so asparagine has only one basic group, the α-NH₂.
Threonine	T	$\mathrm{-CH(OH)CH_3}$	Neutral	Yes
Serine	S	$\mathrm{-CH_2OH}$	Neutral	No
Cysteine	C	$\mathrm{-CH_2SH}$	Neutral	No
Methionine	M	$\mathrm{-CH_2CH_2SCH_3}$	Neutral	Yes
Phenylalanine	F	$\mathrm{-CH_2C_6H_5}$	Neutral	Yes
Tyrosine	Y	$\mathrm{-CH_2C_6H_4OH}$ (para)	Neutral	No
Tryptophan	W	$\mathrm{-CH_2}$ -indolyl, two fused rings, one with N	Neutral	Yes
Histidine	H	$\mathrm{-CH_2}$ -imidazolyl, a five-membered ring with two N	Basic	Yes
Proline	P	$\mathrm{-CH_2CH_2CH_2-}$ joined back to the α-N, a five-membered ring	Neutral	No

Ten are essential. The letters that are not the first letter of the name are D, E, N, Q, K, R, F, W and Y.

Tests for amino-acid side chains and the ninhydrin test

Amino acid	Side-chain group	Test	Result
Tyrosine	Phenolic OH	Neutral FeCl₃	Violet colour
Serine, threonine	Alcoholic OH	Ceric ammonium nitrate	Red colour
Lysine	Primary amine, $\mathrm{-NH_2}$	Hinsberg's reagent, $\mathrm{C_6H_5SO_2Cl}$	Sulphonamide that dissolves in alkali
Glutamine, asparagine	Primary amide, $\mathrm{-CONH_2}$	Hoffmann bromamide, $\mathrm{Br_2}$ with NaOH	Amine with one carbon fewer
Tyrosine, tryptophan, phenylalanine	Benzene ring	Xanthoproteic, concentrated $\mathrm{HNO_3}$	Yellow colour
Every α-amino acid and protein	Free α-amino group	Ninhydrin	Purple colour

Match the group in the side chain first; the test follows from the group.

Common traps

Aspartic acid is D, asparagine is N

A is alanine, so neither Asp nor Asn gets it. The acid takes D and the amide takes N; glutamic acid is E and glutamine is Q in the same way.

Tyrosine is not essential

The body makes tyrosine from phenylalanine, so tyrosine is non-essential while phenylalanine is essential. Proline is non-essential too.

Proline's ring is five-membered, and histidine has a ring

Proline's ring holds four carbons and the N. Histidine carries an imidazole ring, a heterocycle, so a statement that histidine has no heterocyclic ring is false.

Not every chiral amino acid has one stereocentre

Threonine and isoleucine each have two. A statement that all naturally occurring amino acids except glycine have exactly one chiral centre is false.

Amino acids are salts, not organic liquids

As dipolar ions they are crystalline, high-melting and water soluble, and they do not dissolve in benzene. A statement that arginine is highly soluble in benzene is the false one.

Protein hydrolysis gives α-amino acids

Every amino acid from a protein has its NH₂ on the α-carbon. Options with β, γ or δ amino acids describe no natural protein.

Lysine carries an amine, glutamine an amide

Lysine's side chain ends in NH₂ on a CH₂, a primary amine, so it answers Hinsberg's test. Glutamine's ends in CONH₂, a primary amide, so it undergoes Hoffmann bromamide degradation.

Ferric chloride needs a phenol

Serine and threonine have alcoholic OH and give no FeCl₃ colour. Only tyrosine, with its phenolic OH, gives the violet colour.

Peptides and Protein Structure

Learn this subtopic in the notes

Counting peptide bonds and peptide sequences

Peptide bonds, sequences and minimum molar mass

n_{\text{peptide bonds}} = n - 1 \qquad N_{\text{no repeats}} = n! \qquad N_{\text{repeats allowed}} = k^{\,n} \qquad M_{\min} = \frac{M \times 100}{p}

Reading and writing peptide sequences

A dipeptide, written N-terminal first

\mathrm{H_2N{-}CH(R_1){-}CO{-}NH{-}CH(R_2){-}COOH} = \text{residue 1-residue 2}

Levels of protein structure and denaturation

Level	What it describes	Held by	After denaturation
Primary	The sequence of amino acids in each chain	Peptide (covalent amide) bonds	Intact
Secondary, α-helix	The chain coiled into a right-handed spiral	Hydrogen bonds between the C=O and N–H of peptide bonds on neighbouring turns	Lost; the helix uncoils
Secondary, β-pleated sheet	Chains stretched out and laid side by side	Hydrogen bonds between the C=O and N–H of neighbouring chains	Lost
Tertiary	The overall folding of the chain, which gives the fibrous or globular shape	Hydrogen bonds, disulphide links, van der Waals and electrostatic forces	Lost; globules unfold
Quaternary	The spatial arrangement of two or more polypeptide subunits	The same weak forces acting between the subunits	Lost

Only the primary structure is held by covalent peptide bonds, and only it survives denaturation.

Common traps

A chain has a direction

Gly-Ala has glycine at the free NH₂ end and Ala-Gly has alanine there; they are different compounds. Count ordered arrangements (n!), not unordered choices.

n residues make n − 1 bonds

Seven residues are held by six peptide bonds, not seven. The last residue's COOH stays free.

The biuret test needs two peptide bonds

Glycine has none and glycylalanine has one, so neither gives the violet colour. A tripeptide and biuret itself do.

Read from the free NH₂ end

A drawn peptide read from the COOH end gives the sequence backwards: FLDY would come out as YDLF. Find the free NH₂ first.

The acid chloride belongs to the first residue

To make Gly-Ala, glycine supplies the COCl and alanine the free NH₂. The reverse pairing, glycine's COOH with alanine's COCl, gives Ala-Gly.

Quaternary structure is not the overall fold

The overall folding of one chain is the tertiary structure. The quaternary structure is how separate subunits pack together.

Denaturation keeps the peptide bonds

Boiling an egg destroys the secondary and tertiary structures but breaks no peptide bond, so the primary structure stays. A statement that heating breaks the peptide linkages is false.

Fibrous proteins are the insoluble ones

Keratin, collagen and myosin are fibrous and insoluble; albumin and insulin are globular and soluble. Acids denature the soluble globular form, not a soluble fibrous one.

Enzymes and Vitamins

Learn this subtopic in the notes

Enzymes and the reaction each one catalyses

Enzyme	Converts	Into	Source or site
Invertase	Sucrose (cane sugar)	Glucose and fructose	Yeast
Zymase	Glucose	Ethanol and carbon dioxide	Yeast
Diastase	Starch	Maltose	Malt (germinating barley)
Maltase	Maltose	Glucose	Yeast
Urease	Urea	Ammonia and carbon dioxide	Soya bean
Pepsin	Proteins	Peptides	Stomach
Trypsin	Peptides and proteins	Amino acids	Pancreas, acting in the intestine

Starch goes to maltose (diastase), then to glucose (maltase), then to ethanol (zymase).

Vitamins: chemical names, deficiency diseases and sources

Vitamin	Chemical name	Deficiency disease	Main sources
A	Retinol	Xerophthalmia (hardening of the cornea) and night blindness	Fish liver oil, carrots, butter, milk
B1	Thiamine	Beri-beri (loss of appetite, retarded growth)	Yeast, milk, green vegetables, cereals
B2	Riboflavin	Cheilosis (fissures at the corners of the mouth and lips), digestive disorders	Milk, egg white, liver, kidney
B6	Pyridoxine	Convulsions	Yeast, milk, egg yolk, cereals, grams
B12	Cyanocobalamin	Pernicious anaemia	Meat, fish, egg, curd
C	Ascorbic acid	Scurvy (bleeding gums)	Citrus fruits, amla, green leafy vegetables
D	Calciferol	Rickets in children, osteomalacia in adults	Sunlight, fish, egg yolk
E	Tocopherol	Increased fragility of red blood cells, muscular weakness	Vegetable oils such as wheat germ and sunflower oil
K	Phylloquinone	Increased blood clotting time	Green leafy vegetables

B1, B2 and B6 are the pairs most often swapped: thiamine, riboflavin, pyridoxine.

Common traps

Maltase, not oxidase, hydrolyses maltose

Enzymes are named for what they act on. The hydrolysis of maltose to glucose is catalysed by maltase; an oxidase catalyses an oxidation.

Diastase stops at maltose

Diastase converts starch into maltose, not glucose. Maltase takes maltose on to glucose, and zymase takes glucose to ethanol and CO₂.

Enzymes are specific

Each enzyme catalyses one reaction or one class of reaction. A statement that enzymes are non-specific and catalyse different kinds of reactions is false.

B12 is water soluble but stored

Do not drop B12 when counting storable vitamins. The count is the four fat-soluble vitamins plus B12.

Thiamine and ascorbic acid are not stored

Thiamine is B1 and ascorbic acid is C; both are water soluble. Of the common pairs, vitamins A and D are the ones stored for a long time.

Thiamine, riboflavin, pyridoxine in order

B1 is thiamine, B2 riboflavin and B6 pyridoxine. Their diseases follow the same order: beri-beri, cheilosis, convulsions.

Vitamin K deficiency slows clotting

Without vitamin K blood takes longer to clot, so the clotting time increases. An option saying it decreases is false.

Nucleic Acids

Learn this subtopic in the notes

Base pairing and counting hydrogen bonds in DNA

Hydrogen bonds in a DNA double helix

N_{\text{H-bonds}} = 2\,n_{\mathrm{A=T}} + 3\,n_{\mathrm{G\equiv C}}

Nucleosides, nucleotides and the bases and sugars of DNA and RNA

Component	Kind	In DNA	In RNA
Adenine (A)	Purine base, two rings	Yes	Yes
Guanine (G)	Purine base, two rings	Yes	Yes
Cytosine (C)	Pyrimidine base, one ring	Yes	Yes
Thymine (T)	Pyrimidine base, 5-methyluracil	Yes	No
Uracil (U)	Pyrimidine base	No	Yes
β-D-2-Deoxyribose	Pentose sugar, furanose ring	Yes	No
β-D-Ribose	Pentose sugar, furanose ring	No	Yes
Phosphate	Joins C-5′ of one sugar to C-3′ of the next	Yes	Yes

Thymine and deoxyribose mark DNA; uracil and ribose mark RNA.

Common traps

The nucleic-acid sugar is a β furanose

Ribose and 2-deoxyribose sit in nucleic acids as five-membered β-D rings. A statement that the sugar is a pyranose, or the α anomer, is false.

Nucleotides are joined by phosphodiester links

The glycosidic link joins the base to C-1′ of its own sugar. Nucleotide to nucleotide is a phosphodiester link between C-5′ and C-3′, not a C-1 to C-4 glycosidic link.

Chirality comes from the sugar

The bases are flat and the phosphate is not a stereocentre. DNA and RNA are chiral because every unit carries a D-sugar.

Count one strand, not both

Each base of the given strand already stands for one base pair. Counting the complementary strand as well doubles the answer.

RNA makes the proteins

DNA carries the message for protein synthesis, but the proteins are made by RNA. Statements that DNA synthesises proteins, or that RNA is the reserve of genetic information, are false.

Biomolecules formulas

Monosaccharides: Classification and Glucose Reactions

Reactions that prove the open-chain structure of glucose

Classes of carbohydrates and their colour tests

Common traps

Cyclic Structures, D/L Configuration and Anomers

D/L configuration from the Fischer projection

Cyclic structures, anomers and epimers of glucose and fructose

Common traps

Disaccharides, Polysaccharides and Reducing Sugars

Glycosidic linkages in sucrose, maltose and lactose

Starch, glycogen and cellulose: linkages and sources

Common traps

Amino Acids: Essential, Codes and Properties

Structure, dipolar ion and chirality of α-amino acids

The twenty amino acids: codes, side chains and the essential ones

Tests for amino-acid side chains and the ninhydrin test

Common traps

Peptides and Protein Structure

Counting peptide bonds and peptide sequences

Reading and writing peptide sequences

Levels of protein structure and denaturation

Common traps

Enzymes and Vitamins

Enzymes and the reaction each one catalyses

Vitamins: chemical names, deficiency diseases and sources

Common traps

Nucleic Acids

Base pairing and counting hydrogen bonds in DNA

Nucleosides, nucleotides and the bases and sugars of DNA and RNA

Common traps

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